The U.S. now ranks 26th out of 35 for overall life expectancy among other developed and developing countries. PROBLEM: Sedentary lifestyle increases the risk of 40 chronic diseases. Most (?97%) adults do not meet U.S. guidelines for weekly physical activity, thereby increasing the onset of chronic disease, beginning at a younger age. Understanding the biological proclivity for sedentary living could help identify interventions to increase U.S. life expectancy. Growing evidence suggests that genetics plays a significant role in decreasing the motivation to be physically active. For example, in 772 mono- and di-zygotic twins, data was published showing sedentary behavior is moderately heritable in adults based upon between-twin variation in sedentary behaviors. PRELIMINARY STUDIES: Rats were successfully bred for the phenotype of low voluntarily wheel- running (LVR) motivation and potential gene candidates specific to the nucleus accumbens, a region integral to motivated behaviors, were found. One candidate gene, protein kinase inhibitor alpha (Pki?), was shown to be lowly expressed in LVR compared to outbred, wild-type (WT) rats and was further addressed due to its key position in modulating motivation-related signaling. Local overexpression of the Pki? in the nucleus accumbens of female LVR rats increased voluntary running distances 3.1-fold compared to pair-matched empty vector controls. Amazingly, WT rats did not increase nightly running distance following Pkia overexpression and appeared to show molecular resistance to Pki? overexpression. OBJECTIVES: A better understanding of mechanisms that control the lack of motivation for physical activity behavior can help facilitate the development of potential drug therapies for sedentary individuals and combat age-related decreases in physical activity over the lifespan. As such, the goal of this application is to expand upon these findings and help reverse sedentary lifestyle. STRATEGY: Aim 1 will further test the ability of Pki? overexpression in the nucleus accumbens of wild-type (WT) and LVR rats at 15 and 24 weeks of age to increase voluntary running behavior and the molecular responses in male and female rats. Two hypotheses are that Pki? overexpression in nucleus accumbens will increase voluntary running distance: 1) in young LVR rats, but not WT because of their differences in molecular responses; and 2) in both LVR and WT 24-wk-old rats whose running started less than their younger counterparts. Aim 2 will examine whether differences in either single-nucleotide polymorphisms, methylation, and/or differentially bound transcription-factors exist in the promoter of LVR vs. WT rats in 15- and 24-wk-old rats. The outcome could help to explain the differential expression of Pki? in different rat models that correlate with different voluntary activity behaviors. SIGNIFICANCE: This 2-yr R21 project will advance our understanding of molecular mechanisms responsible for sedentary behavior associated with aging and genetic background. Pki? rescue of running from low voluntary running sets guides for potential therapies to lengthen the desire for vigorous physical activity into old age, thereby increasing health and longevity.